1. Field of the Invention
The present invention relates to an electromagnetic relay suitable for a high-frequency switching.
2. Description of the Related Art
Conventionally, a microstrip line structure is known as an electromagnetic relay suitable for high-frequency switching.
For example, Japanese Unexamined Patent Publication No. 6-12957 discloses an electromagnetic relay for high-frequency switching, in which a movable block disposed on a base having a grounding portion provided at the lower or upper plane of the base drives a movable contact piece at its side to open or close the contact point and thereby to transmit a high frequency signal through signal lines formed of fixed contact pieces and movable contacts.
Generally, in this kind of high-frequency electromagnetic relay, the entire case is composed of shielding plates, or the contact switching portion is covered with a shielding plate, and the shielding plates are grounded to enhance isolation.
However, in an electromagnetic relay which is mounted on a printed wiring board of this kind, a microstrip structure is used to reduce the size. However, since the members are packed at a high density, such as movable iron pieces of driving parts and movable contact pieces in the contact switching parts, the internal space in the electromagnetic relay is limited. Therefore, it is hard to form shielding portions in a wide range around signal lines to heighten isolation in such a small space. If a sufficient shielding structure is achieved, the entire size is increased. Further, if the signal lines including movable contact pieces are apart from the base upward, the loss is increased.
It is therefore an object of the invention to present an electromagnetic relay for high frequency signal switching operations which is small, has high isolation characteristics, and little loss.